1. Field of the Invention
This invention relates to a key board switch structure comprising as a stress transducer element a multiple-piezoelectric polymer film element having a plurality of piezoelectric unit elements provided on the surfaces of a polymer film and adapted so that the changes in the stress signals applied to the piezoelectric unit elements are converted into changes in piezoelectric electric field and taken out as the result of the switching operation.
2. Description of the Prior Art
The basic concept of a key board switch has already been proposed in Japanese Patent Laid Open Application No. 37244/72 wherein a multiple-piezoelectric polymer film element comprising a piezoelectric film, for example, of polyvinylidene fluoride rendered piezoelectric through polarization and a plurality of piezoelectric unit elements distributed in the film having electrodes on both surfaces of the films, with mechanical stress signals being applied to each of the unit elements to produce changes in the piezoelectric field some of the distributed elements and the changes in the piezoelectric field being used for signal input is described.
The example of the foregoing Japanese patent application discloses that when a stress is applied to a unit element of a key board switch, this stress is also transmitted more or less to other elements adjacent thereto resulting in a piezoelectric field but that such a piezoelectric field can easily be distinguished from the piezoelectric field generated from the unit element to which the stress is applied since the level of the former is usually on the order of one tenth of the latter. If the stress applied to the elements is always constant, the piezoelectric output from the unit element to which the stress is applied and the piezoelectric output from the other unit elements adjacent thereto can be distinguished and only the signals from the former unit can be utilized for input by cutting the electric field below this constant value. When the values of the stress are varied significantly as in the case of touching a pushbutton with one's finger, the piezoelectric field generated from a unit element by a low stress sometimes may be comparable to the piezoelectric field generated from the adjacent unit elements when a high stress is applied to the foregoing unit element, and such an electric field in this adjacent unit element forms undesirable noise.